Automatic transmission control system

Abstract

An automatic transmission comprises a metal V-belt mechanism 10 , which changes the speed ratio of the rotational output from an engine ENG, a forward/reverse direction change mechanism 20 , which switches the rotational direction of the ratio-change mechanism, and a forward clutch 30 , which actuates the switching operation of the rotational direction performed by the forward/reverse direction-change mechanism. A control system for this transmission comprises a regulator valve 50 , which generates a line pressure, a manual valve 80 , which is operated in correspondence to the shift lever and switches the supply of the line pressure to the forward clutch, and a drive-range sensor 105 , which detects the operation of the manual valve. When the movement of the manual valve to a position where the line pressure is to be supplied to the forward clutch is detected by the drive-range sensor 105 , the line pressure, which is adjusted by the regulator valve, is lowered for a predetermined time period.

What is claimed is:  
     
       1. A control system for an automatic transmission comprising a ratio-change mechanism characterized by a continuously variable speed control mechanism, which includes a variable width drive pulley, a variable width driven pulley and belt means disposed around these pulleys, for transmitting a rotational driving force from a drive power source in a continuous ration change, a forward/reverse direction-change mechanism, which switches from said drive power source through said ratio-change mechanism, said forward/reverse direction-change mechanism disposed between said drive power source and said continuously variable speed control mechanism, forward/reverse direction-change actuator, which actuates direction-change operation of the forward/reverse direction-change mechanism by receiving a hydraulic pressure, and a starting clutching means for controlling transmission of drive power provided on an output side of said continuously variable speed control mechanism; 
       said control system comprising:  
       a regulator valve, which generates a line pressure by adjusting a hydraulic pressure from a hydraulic pressure source;  
       a manual switching valve, which is operated by an external factor, to switch a supply of oil at said line pressure to said forward/reverse direction-change actuator; and  
       a switching operation detector, which detects movement of said manual switching valve;  
       wherein:  
       when the movement of said manual switching valve to a position where said line pressure is to be supplied to said forward/reverse direction-change actuator is detected by said switching operation detector, said line pressure, which is adjusted by said regulator valve, is lowered for a predetermined time period immediately after this detection to gradually engage said starting clutching means.  
     
     
       2. The control system as set forth in  claim 1 , wherein: when the movement of said manual switching valve to a position where said line pressure is to supplied to said forward/reverse direction-change actuator is detected by said switching operation detector, at first, invalid-stroke clearing, which brings said forward/reverse direction-change actuator into a condition ready to start real actuation, is executed, and then, said line pressure, which is adjusted by said regulator valve, is lowered. 
     
     
       3. The control system as set forth in  claim 1 , wherein: the lowering of said line pressure, which is adjusted by said regulator valve, is executed at first by lowering said line pressure to a predetermined lower value at a predetermined reduction rate and then by maintaining said line pressure at said predetermined lower value for a time period that is set on a line-pressure lower limit timer in correspondence to temperature of oil used in said ratio-change mechanism. 
     
     
       4. The control system as set forth in  claim 1 , further comprising a ratio-controlling actuator, which receives a hydraulic pressure to actuate speed ratio control of said ratio-change mechanism, wherein: 
       said ratio-controlling actuator receives said line pressure to actuate the speed ratio control.  
     
     
       5. The control system as set forth in  claim 1 , further comprising a drive cylinder chamber provided in said drive pulley, a driven cylinder chamber provided in said driven pulley and a shift control valve, which controls a supply of hydraulic pressure to said drive cylinder chamber and said driven cylinder chamber, wherein: 
       said shift control valve controls a supply of oil at said line pressure to said drive cylinder chamber and said driven cylinder chamber.  
     
     
       6. The control system as set forth in  claim 1 , wherein the lowered line pressure is lower then the line pressure which is set at a neutral range of said automatic transmission.